Cardiogenic shock: From ECMO to Impella and beyond

Left-sided Impella: A longer-term temporary support

ECMO is a temporary fix that is usually used only for a few days. If longer support is needed, axillary placement of an Impella should be used as a bridge to recovery, transplant, or a durable LVAD.

The Impella device (Figure 3) is a miniature rotary blood pump increasingly used to treat cardiogenic shock. It is inserted retrograde across the aortic valve to provide short-term ventricular support. Most devices are approved by the US Food and Drug Administration (FDA) for less than 7 days of use, but we have experience using them up to 30 days. They are very hemocompatible, involving minimal hemolysis. Axillary placement allows early extubation and ambulation and is more stable than groin placement.

Several models are available: the 2.5 and 3.5 L/min devices can be placed percutaneously, while the 5 L/min model must be surgically placed in the axillary or groin region. Heparin is required with their use. They can replace ECMO. A right ventricular assist device (RVAD), Impella RP, is also available.

Physiologic impact of the Impella

The Impella fully unloads the left ventricle, reducing myocardial oxygen demand and increasing myocardial blood flow. It reduces end-diastolic volume and pressure, the mechanical work of the heart, and wall tension. Microvascular resistance is reduced, allowing increased coronary flow. Cardiac output and power are increased by multiple means.^8–11

The RECOVER 1 trial evaluated the 5L Impella placed after cardiac surgery. The cardiac index increased in all the patients, and the systemic vascular resistance and wedge pressure decreased.¹²

Unloading the ventricle is critical. Meyns  and colleagues¹³ found a fivefold reduction in infarct size from baseline in a left anterior descending occlusion model in pigs after off-loading the ventricle.

Impella has the advantage of simple percutaneous insertion (the 2.5 and CP models). It also tests right ventricular tolerance: if the right ventricle is doing well, one can predict with high certainty that it will tolerate an LVAD (eg, HeartWare, HeartMate 2 (Pleasanton, CA), or HeartMate 3 when available).

Disadvantages include that it provides only left ventricular support, although a right ventricular device can be inserted for dual support. Placement requires fluoroscopic or echocardiographic guidance.

TandemHeart requires septal puncture

The TandemHeart is approved for short-term and biventricular use. It consists of an extracorporeal centrifugal pump that withdraws blood from the left atrium via a trans-septal cannula placed through the femoral vein (Figure 4) and returns it to one or both femoral arteries. The blood is pumped at up to 5 L/min.

It is designed to reduce the pulmonary capillary wedge pressure, ventricular work, and myocardial oxygen demand and increase cardiac output and mean arterial pressure. It has the advantages of percutaneous placement and the ability to provide biventricular support with 2 devices. It can be used for up to 3 weeks. It can easily be converted to ECMO by either splicing in an oxygenator or adding another cannula.

Although the TandemHeart provides significant support, it is no longer often used. A 21F venous cannula must be passed to the left atrium by trans-septal puncture, which requires advanced skill and must be done in the catheterization laboratory. Insertion can take too much time and cause bleeding in patients taking an anticoagulant. Insertion usually destroys the septum, and removal requires a complete patch of the entire septum. Systemic anticoagulation is required. Other disadvantages are risks of hemolysis, limb ischemia, and infection with longer support times.

The CentriMag (Levitronix LLC; Framingham, MA) is an improved device that requires only 1 cannula instead of 2 to cover both areas.

DEVICES FOR RIGHT-SIDED SUPPORT

Most early devices were designed for left-sided support. The right heart, especially in failure, has been more difficult to manage. Previously the only option for a patient with right ventricular failure was venoarterial ECMO. This is more support than needed for a patient with isolated right ventricular failure and involves the risk of multiple complications from the device.

With more options available for the right heart (Table 3), we can choose the most appropriate device according to the underlying cause of right heart failure (eg, right ventricular infarct, pulmonary hypertension), the likelihood of recovery, and the expected time to recovery.

The ideal RVAD would be easy to implant, maintain, and remove. It would allow for chest closure and patient ambulation. It would be durable and biocompatible, so that it could remain implanted for months if necessary. It would cause little blood trauma, have the capability for adding an oxygenator for pulmonary support, and be cost-effective.

Although no single system has all these qualities, each available device fulfills certain combinations of these criteria, so the best one can be selected for each patient’s needs.

ECMO Rotaflow centrifugal pump: Fast, simple, inexpensive

A recent improvement to ECMO is the Rotaflow centrifugal pump (Maquet, Wayne, NJ), which is connected by sewing an 8-mm graft onto the pulmonary artery and placing a venous cannula in the femoral vein. If the patient is not bleeding, the chest can then be closed. This creates a fast, simple, and inexpensive temporary RVAD system. When the patient is ready to be weaned, the outflow graft can be disconnected at the bedside without reopening the chest.

The disadvantage is that the Rotaflow system contains a sapphire bearing. Although it is magnetically coupled, it generates heat and is a nidus for thrombus formation, which can lead to pump failure and embolization. This system can be used for patients who are expected to need support for less than 5 to 7 days. Beyond this duration, the incidence of complications increases. 

CentriMag Ventricular Assist System offers right, left, or bilateral support

The CentriMag Ventricular Assist System is a fully magnetically levitated pump containing no bearings or seals, and with the same technology as is found in many of the durable devices such as HeartMate 3. It is coupled with a reusable motor and is easy to use.

CentriMag offers versatility, allowing for right, left, or bilateral ventricular support. An oxygenator can be added for pulmonary edema and additional support. It is the most biocompatible device and is FDA-approved for use for 4 weeks, although it has been used successfully for much longer. It allows for chest closure and ambulation. It is especially important as a bridge to transplant. The main disadvantage is that insertion and removal require sternotomy.

Impella RP: One size does not fit all

The Impella RP (Figure 5) has an 11F catheter diameter, 23F pump, and a maximum flow rate of more than 4 L/minute. It has a unique 3-dimensional cannula design based on computed tomography 3-dimensional reconstructions from hundreds of patients.

The device is biocompatible and can be used for support for more than 7 days, although most patients require only 3 or 4 days. There is almost no priming volume, so there is no hemodilution.

The disadvantages are that it is more challenging to place than other devices, and some patients cannot use it because the cannula does not fit. It also does not provide pulmonary support. Finally, it is the most expensive of the 3 right-sided devices.

CASE REVISITED

The patient described at the beginning of this article was extubated on day 12 but was then reintubated. On day 20, a tracheotomy tube was placed. By day 24, he had improved so little that his family signed a “do-not-resuscitate–comfort-care-arrest” order (ie, if the patient’s heart or breathing stops, only comfort care is to be provided).

But slowly he got better, and the Impella was removed on day 30. Afterward, serum creatinine and liver function tests began rising again, requiring dobutamine for heart support.

On day 34, his family reversed the do-not-resuscitate order, and he was reevaluated for an LVAD as destination therapy. At this point, echocardiography showed a left ventricular ejection fraction of 10%, normal right ventricular function, with a normal heartbeat and valves. On day 47, a HeartMate II LVAD was placed.

On postoperative day 18, he was transferred out of the intensive care unit, then discharged to an acute rehabilitation facility 8 days later (hospital day 73). He was subsequently discharged.

At a recent follow-up appointment, the patient said that he was feeling “pretty good” and walked with no shortness of breath.